If the heroes work for Star Fleet, then an officer higher in the chain of command may be all you need. If the heroes are constantly short of money because their Firefly is out of fuel, anyone with an attractive business deal can hire them and send them into adventure. Are the heroes the epitome of goodness, or they are like the A-team? Then any underdog in need or damsel in distress may call upon their aid.
More Than One Patron for The Same Party
But you may also have a more complex team. Maybe the warriors in the group are hired by the city council. But the priest is just there to keep an eye on things for the church, as a kind of Inquisitor. The mage in the group is there because she expects to recover a lost magick item the others have no knowledge of, and she just forces herself into the group as “an advisor”. A half-elven noble may be part of the team too, because he believes in the cause of the city council. And so on.
Patrons don't have to be regular employers or clients. They can also be the damsel in distress, a dead man with a will, or even in some cases the enemy. In a way, if an enemy kidnaps your friends, and you want them back – he's almost a patron. But if he kidnaps your friends and only wants to return them alive if you work for him, he is certainly a patron.
Or have a Player Character as Patron
Also, one or more of the player characters may be a patron for themselves. If the team leader is the Schutzfrau (Lady Protectress) of Soest, and Soest is to be defended, then the Schutzfrau is the patron. If one of the players wants to rob an interstellar bank, and builds his team, he's the patron. And when the heroes want to empty the Tomb of Horrors from it's treasures, they're almost their own patron. Together with the demilich sorceror waiting for them inside.
The nice thing about patrons as story hooks is, that they are generally thinking people. If one way to move the player characters forward does not work, they may try to think of another one. Some patrons may even join the party to make sure what they want happens. In a way they help steer the group the way you'd like them to go. They're a tool to make game mastering easier. And even if the group does not listen to a patron, you'll still have some interesting interaction!